Lubricating oils



, spent.

Faerie.

Patented Oct. 5, 1954 UNITED STATES PATENT OFFICE 2,691,000 LUBRICATINGOILS 13 Claims.

This invention is for improvements in or relating to lubricants whichare to be used under conditions which tend to disrupt the lubricantfilm, which disruption more particularly takes place when the pressurebetween the bearing surfaces is very great.

Where the lubricant is required to lubricate surfaces under the aboveconditions, the film rupture strength becomes more important than thecoeflicient of friction. For example, under the extreme pressuresobtaining in hypoid gears, if the oil film is ruptured, the metalsurfaces will contact one with the other, thereby leading to loss ofeificiency, excessive wear and ultimately to failure of the mechanism.

There have already been provided lubricants which have a highfilm-rupture strength. Such lubricants are generally known in the tradeas extremepressure lubricants.

These extreme-pressure lubricants originally consisted of lubricatingoil which contained sulphur, either in the form of flowers of sulphur oras a colloidal dispersion. The sulphur, however, was liable toprecipitation and it was later proposed to prepare theseextreme-pressure lubricants by treating a fatty oil, for example, ananimal oil, with thionyl-chloride or with similar reagents, such assulphur monochloride, sulphur dichloride, etc, and then to add theproduct of this reaction to a mineral oil.

- A theory as to the action of extreme pressure lubricants has been thatthe sulphur reacts with metallic surfaces and forms a very thin coatingof iron sulphide and that this sulphide film is sufficient to preventthe metallic surfaces coming into contact with one another should thelubricant film be ruptured. If this theory is, in fact, correct, then itis obvious that the sulphur contained in the oil must be in such form asto be capable of reacting with the metallic surfaces which it is desiredto lubricate. On the other hand, the sulphur compound must not be soreactive as to induce corrosion of the surfaces.

A large number of organic compounds have been proposed for use asextreme pressure agents, including various types of organic di andpolysulphides, and the corresponding derivatives of selenium andtellurium. While the higher polysulphides are very effective inincreasing the film rupture strength of the oil in which they aredissolved, they tend to be inherently unstable, corrosive, especially tocopper and cuprous materials, and to exert a pro-oxidant effect upon theoil.

The disulphides, on the other hand, usually possess rather poor extremepressure properties, insufficient to warrant their use except inconjunction with other extreme pressure additives such as organichalogen compounds. Thus, for example, it has been proposed to employamixture of dibenzyl disulphide or of a dialkyl disulphide with a varietyof organic chlorine compounds.

It is an object of the present invention to provide lubricatingcompositions having extreme pressure properties containing additiveswhich do not substantially tend to increase the rate of oxidation of theoils in service.

It is a further specific object of the invention to provide additivescapable of substantially increasing the film rupture strength oflubricating oils for turbines and/or hypoid gears without at same timeincreasing their tendency to oxidise or emulsify with water.

Thus at the present time many oils used for turbine lubrication consistof specially selected mineral oil blends stabilised against oxidation bythe incorporation of antioxidant additives and containing also additivesdesigned to protect fer rous metal parts against rusting or corrosionby, e. g., sea water. It is of course important that additionaladditives, incorporated in such oils for the purpose of enhancing theirextreme pressure properties, should not interfere in any way with thenormal functions of the two foregoing classes of additive. Many turbineoils, especially marine turbine oils used by the Admiralty, arecontrolled as regards oxidation stability, salt water corrosion offerrous metals, demulsification value and corrosive action on cuprousmetals, by a very rigid specification. It is necessary, therefore, thatextreme pressure additives incorporated therein should not adverselyaffect compliance with its clauses.

Many of the more commonly employed extreme pressure additives aredetrimental in one or more respects. Thus chlorine compounds generallytend to promote oxidation and are also prone to hydrolysis with thesubsequent libersubstituted in the alpha position by dior polysulphidegroups, and the corresponding derivatives of selenium or tellurium andmay be represented by the general formula:

where the radical R is an alkyl, aryl or cycloalkyl 3 radical, X issulphur, selenium or tellurium and n is 2, 3 or 4.

The radicals R may contain halogen substituents, although as alreadyindicated the presence of halogen is to be avoided if the compounds areto be used in certain applications, particularly in the turbine oils.

It would appear that the presence of ester groups situated in the alphaposition to the dior polysulphide groups exerts an activating influencewith the consequent production of extreme pressure propertiessubstantially in excess of those obtainable by the use of the simplealiphatic, aromatic or aryl substituted aliphatic dior polysulphides.

According to the present invention a lubricating composition comprises amineral lubricating oil base and a minor proportion, sufficientsubstantially to increase the load-carrying capacity of the oil, of anester of acetic acid substituted in the alpha position by sulphur,selenium or tellurium said ester having the general formula where R, isan alkyl, aryl or cycloalkyl radical which may contain halogensubstituents, X is sulphur, selenium or tellurium and n is 2, 3 or 4.

The invention includes a turbine oil comprising a mineral lubricatingoil base containing agents controlling oxidation stability and corrosionof ferrous metals and including also a minor proportion, sufiicientsubstantially to increase the load-carrying capacity of the oil, of anester of acetic acid substituted in the alpha position by sulphur,selenium or tellurium said ester having the general formula where R isan alkyl, aryl or cycloalkyl radical, X is sulphur, selenium ortellurium and n is 2, 3 or 4.

Specific examples of compounds which may be employed as additives inaccordance with the present invention are Diethyl dithiodiacetateC2H5OOC.CH2S

Di-n-butyl trithiodiacetate C4H0OOC.CH2S

Diphenyl dithiodiacetate OOC.CHz-S It has been found, surprisingly, thatthe presence of substituents such as alkyl groups or ester-substitutedalkyl groups attached to the carbon atom adjacent to the radical Xresults in a considerable loss of load-carrying ability. Thus thepresence of unsubstituted CH2 groups appears to be essential, inaddition to the presence of ester groups in the alpha position in orderto provide the outstanding extreme pressure properties to whichreference has been made.

While it is believed that some, at least, of the additive compoundsreferred to above are new and have not been prepared heretofore, theymay be prepared by methods known to the art. Thus, they may be preparedby the reaction of the corresponding oc-ChlOlO or abromo esters withsodium dior poly-sulphides in alcoholic solution, or by oxidation or thea-mercapto esters to give the corresponding disulphides, or by reactionof the amercapto esters with sulphur dichloride or sulphur mono-chloridein a non-ionising solvent to give the triand tetra-sulphidesrespectively.

Specific examples of additives employed in the present invention andmethods of preparing them are as follows:

EXAMPLE I Preparation of dz'(n-butyl) dithiodiacetate An alcoholicsolution of sodium disulphide was prepared by dissolving 26.4 grams ofsodium sulphide crystals Na2S.9I-I2O and 3.52 grams of sulphur (0.11 molin each case) in 150 mls. of alcohol at the boiling point.

The deep red solution so obtained was cooled to about 30 C. and 28 grams(0.1 mol.) of n-butyl monochloracetate was added dropwise withcontinuous stirring and cooling maintaining the temperature below about60 C.

An almost instantaneous exothermic reaction took place and sodiumchloride was precipitated.

At the conclusion of the reaction the mixture was diluted with water toabout 500 ccs. total volume and the reaction product extracted withpetroleum ether.

After washing the extract with water, it was dried over anhydrous sodiumsulphate, filtered, and the solvent removed by distillation.

The product was a pale yellow liquid with a characteristic odour.

EXAMPLE 11 Preparation of dz'(n-butyl) trithiodiacetate This wasprepared precisely as outlined in Example I, except that twice theamount of sulphur was used.

The product resembled the disulphide in appearance.

By adopting the procedure described in Examples I and II, it has beenfound possible to prepare substantially neutral chlorine-free productswithout difiiculty.

EXAMPLE I11 Preparation of dim-batyl) tetrathiodiacetate 37.05 grams ofn-butyl thioglycollate (0.25 mol.) was dissolved in mls. benzene andcooled below 0 C. in a bath of 50% ice and 50% concentrated hydrochloricacid. 16.88 grams /8 mol.) of sulphur monochloride was dissolved in 50mls. benzene and cooled in the same way.

The n-butyl thioglycollate solution was now added dropwise withstirring, keeping the temperature below 0 C. A brisk reaction took placewith evolution of hydrogen chloride. After standing for two hours, themixture was allowed to warm up to room temperature, the evolution ofhydrogen chloride continuing for some hours. The solvent was removed ata temperature not exceeding 25 C.

The product was a yellow liquid.

By methods analogous to those described in Examples I and II, it hasbeen found possible to prepare a variety of. compounds falling withinthe scope of the present invention, some examples of which are asfollows:

Diethyldithiodiacetate, prepared by the method of Example I from ethylmonochloracetate.

(A mixture of the diand trisulphides in approximately 3:1 ratiocontaining 29.0% sulphur was actually made.)

Di (2-ethyl hexylltrithiodiacetate, prepared similarly from 2-ethylhexyl. monochloracetate (as in Example II).

Dicyclohexyl dithiodiacetate, prepared similarlyfrom cyclohexylmonochloracetate.

Di tB-chloroethyl) dithiodiacetate prepared similarly frompl-chloroethyl chloracetate, which was prepared by reacting chloracetylchloride with ethylene chlorhydrin.

Analysis showed that this product was a mixture of compounds formed bythe replacement of some of the terminal chlorine atoms by disulphidegroups.

Aryl esters such as diphenyl dithiodiacetate cannot readily be preparedby the foregoing methods as hydrolysis of the esters appears to takeplace. They may, however, be prepared via the Bunte salts by a. methodsimilar to that described by Stoner and Dougherty in the Journal of theAmerican Chemical Society, vol. 63, p. 987 (1941). Thus, for example,phenyl monochloracetate may be reacted in boiling 50 aqueous alcoholwith sodium thiosulphate, and the product converted tov the disulphideby the addition of iodine.

Yields are usually rather poor and it is therefore generally preferredto employ the alkyl or cycloalkyl esters.

Selenium compounds such as di(nbuty1) diseleno-diacetate may be preparedby reacting the a-halo ester e. g. n-butyl, monochloracetate with sodiumor potassium selenosulphate in aqueous alcoholic solution by the methodemployed by Stoner and Williams in the Journal of the American ChemicalSociety, vol. 70, page 1113 (1948).

The additives used will of necessity be soluble in the mineral oil basein the proportions in which they are to be employed. The preferredcompounds are those which are miscible with oil in all proportions,although others of lower solubility may be satisfactorily used. The oilsolubility will necessarily depend upon the nature of the groups R butin general complete miscibility with. oil. may be achieved by employingas radical R an aliphatic or cycloaliphatic radical having not less thanfour carbon atoms.

The. amounts of the additives employed. will depend upon the purpose forwhich the oil is to be. used. Any quantity from the minimum suflicientto impart a substantial increase in film rupture strength up to aboutper cent may be employed, but in general from about 0.5. per cent. toabout 2.0 per cent is contemplated, especially for use in turbine oils.

The so-called inhibited turbine oils to which the compounds of thisinvention may be added normally contain antioxidant additives which maybe of. the alkylated phenol type, e. g,.,, tertiary butyl cresol, 2.14dimethyl-B-tertiary butyl phenol, 2:6 di-tertiary butyl-p-cresol, orsec.- ondary aromatic amines, e. g., diphenylamine,

6 phenyl a naphthylamine, phenyl-s-naphthylamine, and also anti-rustingadditives which may be of various types, one preferred class ofadditives being the acid esters of the long-chain mono esters. ofpolyhydric alcohols described in patent application No. 191,166.

Some of the additives contemplated, notably the triand higherpolysulphides, tend to be somewhat corrosive to copper and cuprousalloys at. elevated temperatures. In. such cases, it is desirable toincorporate also a copper stain inhibitor of the type disclosed inPatent No. 2,414,257, e. g., mercaptobenzothiazole,benzothiazoledisulphide, benzothiazole hydroxymethyl sulphide, ortetramethyl or tetraethyl thiuram disulphide.

The additives of the present invention may, if desired, be employed inconjunction with organic halogenated compounds in mineral lubricatingoils to provide, for example, extreme pressure lubricants for hypoidgears. Oils containing such combinations of additives are capable ofwithstanding higher loads than oils which contain only the sulphurcompound. As already stated, however, the presence of halogen compoundsin turbine oils is undesirable.

To demonstrate the effectiveness of the compounds of the presentinvention as extreme pressure agents, tests were carried out on thewellknown Society of Automotive Engineers (S. A. E.) Testing Machine, adescription of which may be found in the Co-ordinating Research Council(C. R. C.) Handbook (1946) on pages 458-462. This machine was operatedat 500 R. P. M. using a standard loading rate of 75 to lbs/sec. andrubbing ratio of 14.6:1.

The additives were dissolved in a mineral oil blend (oil A) consistingof 70%. of a mineral .oil having a viscosity of about 170 secondsRedwood at 140 F. and 30% of a solvent refined mineral oil having aviscosity of about 65 seconds Redwood at 140 F.

The results obtained are. tabulatedv below, the. failure loads recordedbeing in general the mean of several tests.

Certain other closely related compounds were tested at the same time inorder to demonstrate the superiority of the compounds of the presentinvention. In the majority of instances the percentages of additive usedwere adjusted to.- provide an. amount of added sulphur of between 0.23and 0.28 per cent.

Percent Sulphur Percent provided Fallureload (lbs), by the additiveCompound Dibenzyl disulphlde 26 Dibenzyl trisulphide E 25 125. (31.7%Diphenyl disulphide... Di(n-butyl) monothiodie etat c e. Di(n-butyl)diB-thiodipropionate.

l2. Di(n-butyl)dithiob.is

(ha-dimethyl) diacetats.

32 scattered results not exceeding 120.

I? This. compound hadv a rather limited oil-solubility.

It will be apparent from the foregoing tests that the compounds of thepresent invention (numbers 2 to 6) possess a marked advantage over:

(a) Conventional diand polysulphides (numbers 7 to 9);

(b) The corresponding monosulphides (number 10) (c) A closely relatedester containing a disul- 8 of the oils to stain copper under theconditions of the standard copper strip corrosion test (I. P. 64/51,Procedure C, page 550, 1951 edition), i. e., immersion for 3 hours at100 C., it has been found necessary in general to employ a copper staininhibitor of the type already described, examples of satisfactorycombinations of additives having been quoted in the foregoing table. Inthis connection it is generally phide group in the ,B-position to theester group 10 preferred to use the diand. tri-sulphides since insteadof the a-position (number 11), and the activity of the sulphur in thetetra-sulphides (d) A compound containing alkyl substituents is greaterand more difficult to control. attached to the disulphide group (number12). Comparative tests on certain of the oils were In order to obtainthe best results, it would obtained by the use of a high speed disctestappear desirable to have the radicals R consist- 15 ing machine inwhich two discs of En. 36 caseing of relatively short alkyl chains, theintrohardened steel of diameter 8 and 4", respecduction of large orcyclic groups tending to retively, were rotated in contact with oneanother duce load-carrying capacity. Thus it is preat speeds of 1800 and7200 revolutions per minferred that the radicals R shall consist ofalkyl ute, respectively, the sliding velocity being 3775 radicals havingnot more than six carbon atoms. feet per minute. The discs were immersedin To illustrate the effectiveness of the comthe oil under test, whichwas maintained at pounds of the present invention when employed 155-165F., and the load on the discs was gradfor the purpose of impartingextreme pressure ually increased until scuffing took place. Theproperties to turbine oils, an inhibited turbine results were recordedas Sc loads at the incioil nf rm t B t sh Ad ty p fi adence of scuffing,the definition of the term Sc tion OM.88 was selected (oil B). Thisconsisted being: of an oil similar to oil A. containing 0.5% of a psecondary aromatic amine type oxidation in- Poundshgdl i g ofhneoosfContact hibitor and 0.07% of a ferrous metal corrosion eatlve curvature)inhibitor consisting of ethylene glycol mono- Six tests were carried outon each of the oils naphthenate acid phthalate. tabulated below, and themean Sc loads quoted The following table illustrates the effect of foreach oil. Oil C was a typical turbine oil of additives of the presentinvention on the propsimilar viscosity to oil B and containingantierties of oil B: oxidant and rust inhibitors.

Oxidation Test Acidity, Demulsi- Salt Water u Additives milligramsfication Add Demulsi- Corrosion KOH/gm. value after ficatiou R P M) damwill??? Seconds Seconds 1. None N 0.08 180 0.17 540 No rusting 150 2.Diethyl-dithio-diacetate (2%) 0.17 195 340 3. Di(n butyl)trithiodiacetete (1.5%) 0.08 180 0.14 330 No rusting" 250 bcnzothiazoledisulphide (0.1%).

4. Di(n-butyl)trithio-diacetate 1.0%) 0.20 130 0.17 480 do 21smercaptobenzothiazole (0.05%). 5. Dicyclohexyl dithio-diacetate (1.5%)0.08 135 6. Di(n-butyl)dlseleno-diacetatc (1.0%) 0.15 150 0.08 225 Veryslight benzothiazolc disulphide (0.1%). rusting.

1 The somewhat high acidity in this instance was due to the presence ofa trace of acid in the additive.

The methods employed for determining the various values quoted abovewere standard methods described in the Standard Methods for TestingPetroleum and its Products, and having the following references:

Acidity, I. P. 1/46, Method A (page 11951 edition).

Demulsification value, I. P. 19/51 (page 117- 1951 edition).

Oxidation test, I. P. 114/47 (page 363--1951 edition).

Salt water corrosion test, I. P. 125/51 (1951 edition, page 390)(modified in respect of salt water composition and duration, to complywith the requirements of British Admiralty Specification OM88).

It will be seen from the foregoing tests that the additives of thepresent invention not only greatly enhanced the load-carrying capacityof the turbine oil in which they were dissolved, but also leftunaffected the essential properties of the oil, i. e., low acidity, lowdemulsification value, high resistance to oxidation and ability toinhibit corrosion of ferrous metals by salt water.

In order to eliminate completely all tendency In the case of oils 2 and3, no scuffing was experienced in three and six tests, respectively, upto a limit of 12,550 lbs., after which the tests were discontinued. Theother three tests on oil '2 were terminated at lower Sc loads, withoutany scufiing having occurred.

To provide illustrations of lubricating oil compositions suitable foruse as extreme pressure lubricants for hypoid gears, compounds of thepresent invention were dissolved in a relatively viscous mineral oilblend designated oil D, which consisted of 27 parts by weight of aconventionally refined Pennsylvanian bright stock of viscosity 600seconds Redwood at F., 34 parts of a conventionally refinedMid-Continent Failure Oil 2% Di(n-butyl) dithiodiacetate. 0.2%Mercaptobenzothlazol 91.9% Oil D B Hexachlorethaue 89.8% our) 3%DMZ-ethyl hexyl) trlthiodiacetatei: 0.1% Tetraethyl thiuramdisulphide..."

The normal requirement for a good extreme pressure lubricant for hypoidgears is that it should withstand loads up to 350 lbs. under theseconditions.

I claim:

1. A lubricating composition comprising a mineral oil containing a smallamount sufficient to increase the load-carrying capacity of the oil ofan ester of acetic acid substituted in the alpha position by an elementselected from the group consisting of sulphur and selenium, said esterhaving the general formula in which R is a radical selected from thegroup consisting of alkyl, aryl and cycloalkyl radicals, X is an elementselected from the group consisting of sulphur and selenium and n is aninteger from 2 to 4 inclusive.

2. A lubricating composition comprising a mineral oil containing a smallamount suflicient to increase the load-carrying capacity of the oil ofan ester of acetic acid substituted in the alpha position by an elementselected from the group consisting of sulphur and selenium, said esterhaving the general formula ROOC.CH2 (X) n-CH2-COOR in which R is achlorine containing radical selected from the group consisting of alkyl,aryl and cycloalkyl radicals, X is an element selected from the groupconsisting of sulphur and selenium and n is an integer from 2' to 4inclusive.

3. A lubricating composition comprising a mineral oil containing about0.5% to about by weight of an ester of acetic acid substituted in thealpha position by an element selected from the group consisting ofsulphur and selenium, said ester having the general formula in which Ris a radical selected from the group consisting of alkyl, aryl andcycloalkyl radicals, X is an element selected from the group consistingof sulphur and selenium and n is an integer from 2 to 4 inclusive.

4. A lubricating composition comprising a mineral oil containing from0.5% to 2.0% by weight of an ester of acetic acid substituted in thealpha position by an element selected from the group consisting ofsulphur and selenium, said ester having the general formula ROOC.CH2 (X)n-CH2COOR ll) in which R is a radical selected from the group consistingof alkyl, aryl and cycloalkyl radicals, X is an element selected fromthe group consisting of sulphur and selenium and n is an integer from 2to 4 inclusive.

5. A lubricating composition comprising a mineral oil containing a smallamount suflicient to increase the load-carrying capacity of the oil ofan ester of acetic acid substituted in the alpha position by an elementselected from the group consisting of sulphur and selenium, said esterhaving the general formula in which R is an alkyl radical containing notmore than six carbon atoms X is an element selected from the groupconsisting of sulphur and selenium and n is an integer from 2 to 4inclusive.

6. A lubricating composition comprising a mineral oil containing from0.5% to 2.0% by weight of an ester of acetic acid substituted in thealpha position by an element selected from the group consisting ofsulphur and selenium, said ester having the general formula ROOC.CH2-(X) n--CH2.COOR

in which R is an alkyl radical containing not more than six carbon atomsX is an element selected from the group consists of sulphur and seleniumand n is an integer from 2 to 4 inclusive.

7. A lubricating composition as claimed in claim 1 in which there isalso incorporated a small amount of a compound selected from the groupconsisting of mercapto-arylene-thiazoles and derivatives ofmercapto-arylene-thiazoles.

8. A lubricating composition as claimed in claim 1 in which there isalso incorporated a small amount of an alkyl thiuram disulphide.

9. A lubricating composition as claimed in claim 1 in which there isalso incorporated a small amount of berizothiazole disulphide.

10. A lubricating composition comprising a mineral oil containing as anadditive from 0.5% to 2.0% by weight of di(n-butyl) dithiodiacetate.

11. A lubricating composition comprising a mineral oil containing as anadditive from 0.5% to 2.0% by weight of di(n-butyl) trithiodiacetate.

12. A turbine oil comprising a mineral oil containing agents controllingoxidation stability and corrosion of ferrous metals and including also asmall amount suificient to increase the load-carrying capacity of theoil of an ester of acetic acid substituted in the alpha position by anelement selected from the group consisting of sulphur and selenium, saidester having the general formula ROOC.CH2 (X) n-CHaCOOR in which R is aradical selected from the group consisting of alkyl, aryl and cycloalkylradicals, X is an element selected from the group consisting of sulphurand selenium and n is an integer from 2 to 4 inclusive.

13. An extreme pressure lubricant comprising a lubricating oilcomposition as claimed in claim 1 and including in addition to the esterof acetic acid an organic halogenated compound.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,073,841 Humphreys Mar. 16, 1937 2,317,666 Burwell Apr. 27,1943 2,467,303 Frank Apr. 12, 1949 2,503,401 Mattano et al Apr. 11, 19502,649,416 Richter et a1 Aug. 18, 1953

1. A LUBRICATING COMPOSITION COMPRISING A MINERAL OIL CONTAINING A SMALLAMOUNT SUFFICIENT TO INCREASE THE LOAD-CARRYING CAPACITY OF THE OIL OFAN ESTER OF ACETIC ACID SUBSTITUTED IN THE ALPHA POSITION BY AN ELEMENTSELECTED FROM THE GROUP CONSISTING OF SULPHUR AND SELEMIUM, SAID ESTERHAVING THE GENERAL FORMULA